Bistable thermo-responsive device



March 16, 1965 H. G. snBERG 3,174,013

BISTABLE THERMO-RESPONSIVE DEVICE:

Filed Aug. 25, 1961 ATTO R N EYS United States Patent O 3,174,013 ESTABLE THERMO-RESPONSIVE DEVICE Hemming G. Siiberg, Westfield, NJ., assignor to Tung- Sol Electric Inc., a corporation of Delaware Filed Aug. 25, 1961, Ser. No. 133,905 9 Claims. (Cl. 200-4122) The present invention relates to thermo-responsive Snap action switches wherein expansion and contraction of iiexible wires or ribbons actuate circuit controlling contacts and comprises a novel switch of this type which is suitable for use as a ilasher or alternator.

The new switch is of simple construction and is positive in operation. When used as a asher the switch maintains a constant ratio of on to off time. When used as an alternator the switch maintains equal on7 time for the lamps or other loads to be alternately energized.

Most wire controlled switches now in public use are of the type wherein an inherent constraint or deformation in a buckling member biases the member toward one position and the pull wire or ribbon, when cold, holds the member out of such biased position, expansion of the pull wire or ribbon permitting the member to snap toward its said biased position. The snap action device of Schmidinger Reissue Patent No. 24,023, dated June 14, 1955, is an example of such type of prior art switch.

As distinguished from the above descr-ibed type of prior art switch which incorporates a mono-stable buckling member having a single pull wire or ribbon, the snap action device of the present invention comprises a bistable buckling member which snaps from one stable position to another in response to alternate contraction of two pull wires or ribbons. As this device during operation is controlled solely by the rate of cooling of the pull wires or ribbons a constant ratio between the dwells in each stable position may be maintained over a relatively Wide range of applied voltage or current.

In the preferred embodiment of the invention, the new switch comprises a `vane of spring metal, preferably of rectangular shape, that is apertured at its center and provided with two parallel longitudinal creases or bends which extend from the aperture to one side edge of the member, one crease or bend being convex toward one surface of the member and the other being concave toward that surface. A pair of spaced Contact carrying pull ribbons, parallel to the creases, extend over opposite surfaces of the member and are fastened under tension to the side edges of the member, each ribbon when cold opposing the deformation introduced into the buckling member by the adjacent crease. Fixed contacts engageable by the ribbon carried contacts and support means for the member and for the xed contacts complete the device.

For a better understanding of the invention and of the advantages thereof, reference may be had to the accompanying drawing of which:

FIG. l is a plan View of a buckling member suitable for use in the snap action device of the invention;

FIG. 2 is a sectional View of the buckling member of FIG. l taken along the line 2 2 thereof;

FIG. 3 is a side View of a snap action device embodying/the invention and incorporating the buckling member of FIGS. l and 2;

FGS. 4 and 5 are plan and side views of the device ice of FIG. 3 taken on the lines 4-4 and 5-5 respectively; and

FIG. 6 is an isometric View of a snap action device similar to that of FIGS. l through 5 but showing indirect heating of one of the pull ribbons.

As shown best in FlGS. l and 2 the buckling member or blade 2 of the new snap action device comprises a generally rectangular sheet of resilient metal, such as spring steel, provided with a central aperture 4 and two creases or bends 6 and v8 which extend from the aperture 4 to one side edge of the blade, crease 6 being convex upward and crease S being concave .as viewed in FIG. l, the creases causing the surface of the blade to be stepped from one plane to another. A pull ribbon 1t) overlies the blade 2 and is welded under tension to the opposite side edges of the blade, the edges of the blade being bent if necessary to provide the desired tension in the ribbon. The ribbon 10 tends to curve the underlying section of the blade about artransverse axis extending through the aperture and at right angles to the -bend 6. Similarly a pull ribbon 12 is positioned on the underside of the blade 2 between the crease 8 and the adjacent longer edge or" the blade. The pull ribbon 12 is likewise secured under tension to the opposite edges of the blade and tends to curve the overlying section of the blade about a transverse axis perpendicular to the crease 8 and passing through the aperture 4. Thus the tension in the pull ribbon 10 tends to make 'the upper surface of the blade concave upwardly and the tension in the ribbon 12 tends to make the upper surface of the blade convex upwardly. A Contact 14 is mounted on the pull ribbon 10 and a similar contact 16 is mounted on the pull ribbon 12. After assembly of the blade with the ribbons attached thereto and the tension thereof adjusted, as by bending of the side edges of the blade, the blade is mounted adjacent the uncrea'sed edge on a fixed C-shaped bracket 18, the lower leg of which is mounted on a suitable base 20 of insulating material. The underside of the blade is welded to the upper leg of bracket 1S and a leaf spring 21 is welded to the upper surface of the blade, the leaf spring 21 extending from the bracket to aperture 4 and serving to oppose flexing movement of the left half of the vane, as viewed in FIG. 4.

A terminal 22 which extends through the base 20 is connected with the support bracket 18. A second terminal 24 is secured in arecess in the wall of the base 20 and carries on its upper end a support arm 26 for a fixed contact 28 positioned for engagement with contact 16 on the pull ribbon 12. A third terminal 30 is mounted in a recess on the opposite side of the base 20 from terminal 24 and carries at its upper enda support arm 32 for a fixed contact 34 positioned for engagement with contact 14 on pull ribbon itl.

When the device is to be used as an alternator, terminal 22 may be connected to the source of potential as indicated by the plus sign in FIG. 5 and terminals 24 and 30 may be respectively connected through loads, illustrated as lamps 36 and 38, to the other terminal of the source, indicated by the ground symbol.

In operation of the device of FlGS. 1 through 5 the xed contacts are so positioned that when the device is cold at least one pair of contacts are in engagement, say contacts 14 and 34. When the circuit is closed as by means of a switch S between `the source and terminal Z2 current will iiow through pull ribbon It), contacts 14 and 34 and through the lamp 38. Pull ribbon 10 will thereupon expand, unbalancing the blade and causing it to snap to the other position with consequent opening of contacts 14 and 34 and closing of contacts 16 and 28. Lamp 36 then lights as its circuit including ribbon i2 is closed at contacts 16 and 28. While ribbon 12 is heating ribbon 10 is cooling. After cooling to a certain temperature the tension in ribbon 10 will be sufficient to snap the blade back to its starting position. rThe cycle then repeats. Once the cycle has been initiated the cooling of the pull ribbons controls the cycling rate and as both ribbons cool at the same rate the ratio of the dwells of the blade in each position will be maintained constant irrespective of voltage variations of the source within the range of l to 16 volts.

in FIG. 6 an alternative arrangement is shown which is particularly suitable lfor use as a asher for automobile turn signals. In this embodiment of the invention the movable arm of a turn signal switch 40 is connected to terminal 24. One xed contact of the switch is connected to left front and rear signal lamps 42 LF and 42 LR and the other fixed contact is connected to right front and rear signal lamps 42 RF and 42 RR. A winding 44 in heat exchange relationship with pull ribbon it) is connected across terminals 24 and 30 and the fixed contact 34 is positioned for engagement with a contact 46 mounted on the blade 2 adjacent the end of pull ribbon 1d. With switch 4t) closed in either direction, when contacts 34 and 46 are in engagement the resistance of winding 44, which is in series with one or the other pair of lamps, is sufiiciently high to prevent illumination of the lamps. The current through the winding is high enough, however, to heat the pull strip it?, permitting the blade to snap to the other position wherein the winding 44 is shunted and full current is delivered to the lamps through pull ribbon 12. Upon consequent cooling of pull ribbon the blade snaps back into position to turn the lamps off. The cycle thereupon repeats.

As the respective on and off periods of the lamps depend only upon the rate of cooling of the pull ribbon and not upon the voltage or current constant ratio of off to on is obtained.

From the foregoing description it will be apparent that the invention comprises a novel thermo-responsive switch incorporating a bistable buckling member controlled in response to alternate cooling of heat expansible pull means. The switch requires relatively yfew parts and is simple to manufacture. it does not require machining to close tolerances, is simple to adjust and is readily incorporated into circuits to be controlled.

Various changes in the specific construction described or in the circuits diagrammatically indicated in the drawings could be made without departing from the spirit of the invention or the scope of the accompanying claims. The parallel creases 6 and 8 which introduce the convex and concave curvatures into the blade tend to stabilize the operation of the device and hence for uniformity in production are preferred. Opposite curvatures could be incorporated in the blade by other means, for examplefby stamping between shaped dies or by slitting and crimping Although the rectangular shape of the blade is preferred, other shapes of the blade such as square or oval, are feasible and shapes of the central opening other than circular could be used. Although the switch has been illustrated in FIG. 5 as connected for operation as an alternator, obviously it could as well be employed as a flasher merely by utilizing one position of the blade for control of a pilot lamp and the other position for control of signal lamps through a `direction switch as in FIG. 6. Similarly, one or more pilot lamps could be provided in the circuit of FIG. 6. For example, a low voltage pilot lamp could be connected to terminal 30 to be lighted alternately with the lamp load, or pilot lamps could be connected to the fixed contacts of switch 40 to be lighted concurrently with the lamp load. Other variations will occur to those skilled in the art.

I claim:

l. A bistable buckling member for a snap action device comprising a vane of electrically conducting resilient material having deformations therein tending to cause parts of the surface thereof to curve oppositely about substantially parallel axes extending towards the edge of the vane from the central portion of the vane, and a pair of heat expansible conductive pull means on the opposite sides of the vane secured under tension to opposite edges of the vane for exerting force along said substantially parallel axes to bow the vane oppositely about an axis transverse to said parallel axes.

2. The bistable buckling member according to claim l wherein said deformations comprise parallel bends in said vane extending from the center of the vane to one side edge thereof.

3. The combination with the bistable buckling member of claim 1 of means including contacts responsive to the position of said vane for alternately heating said pull means.

4. The combination with the bistable member of claim l, of circuit means including fixed contacts and vane carried contacts for engagement therewith for heating one of said pull means when the vane is in one stable position and for heating the other pull means when the vane is in the other stable position, and support means for supporting the bistable member and said fixed contacts whereby the vane is snapped from one stable position to the other in response to cooling of the unheated pull means.

5. A snap action device comprising a vane of electrically conducting resilient material having deformations therein tending to cause parts of the surface thereof to curve oppositely about parallel axes extending towards the edge of the vane from the central portion of the vane, a pair of heat expansible conductive pull means one on each side of the vane secured under tension to opposite edges of the vane for exerting force along said parallel axes, to bow the vane oppositely about an axis transverse to said parallel axes, a pair of fixed contacts, support means for said vane and fixed contacts, a contact carried by said vane and positioned for engagement with one of said fixed contacts when the vane is in one stable position, a second contact carried by said vane and positioned for engagement with the other of said fixed contacts when the vane is in its other stable position, and electrical terminals conductively connected to said vane and to said fixed contacts, at least one of said vane carried contacts being mounted on a pull means.

6. The snap action device according to claim 5 wherein each of said vane carried contacts is mounted on a pull means.

7. The snap action device according to claim 5 including a heater winding in heat exchange relatiosnhip with one of said pull means and connected across said fixed contacts, one of said vane carried contacts being mounted on said vane in a position to engage a fixed contact when the tension in said last mentioned pull means exceeds that in the pull means on which the other vane carried contact is mounted.

8. A snap action device for alternately energizing a pair of load circuits for equal time periods irrespective of change in supply voltage, comprising a vane of electrically conductive material having deformations therein tending to cause parts of the surface thereof to curve oppositely about parallel axes extending towards the edge of the vane from the central portion of the Vane, a pair of heat expansible conductive pull means on opposite sides of the vanes and secured under tension to opposite edges of the vane for exerting force along said axes to bow the vane oppositely about an axis transverse to said parallel axes and together with the deformations causing the vane to have two stable positions, a pair of fixed contacts, support means for said vane and for said fixed contacts, a Contact carried by said vane and positioned for engagement with one of the said fixed contacts when the vane is in one stable position, a second Contact carried by said vane and positioned for engagement with the 5 other of said fixed contacts when the Vane is in its other stable position, and circuit means including a source of energy and said contacts for selectively heating one of 2,322,444 said pull means in each position of said vane, whereby 2,861,149 the vane is snapped from one stable position to the other 10 907,8 50

in response to cooling of the unheated pull means.

9. The bistable buckling member of claim l wherein said pull means are arranged on opposite sides of said substantially parallel axes.

References Cited in the file of this patent UNITED STATES PATENTS Colombo et al. Feb. 4, 1958 Hollis et al. Nov. 18, 1958 Colombo Oct. 6, 1959 

5. A SNAP ACTION DEVICE COMPRISING A VANE OF ELECTRICALLY CONDUCTING RESILIENT MATERIAL HAVING DEFORMATIONS THEREIN TENDING TO CAUSE PARTS OF THE SURFACE THEREOF TO CURVE OPPOSITELY ABOUT PARALLEL AXES EXTENDING TOWARDS THE EDGE OF THE VANE FROM THE CENTRAL PORTION OF THE VANE, A PAIR OF HEAT EXPANSIBLE CONDUCTIVE PULL MEANS ONE ON EACH SIDE OF THE VANE SECURED UNDER TENSION TO OPPOSITE EDGES OF THE VANE FOR EXERTING FORCE ALONG SAID PARALLEL AXES, TO BOW THE VANE OPPOSITELY ABOUT AN AXIS TRANSVERSE TO SAID PARALLEL AXES, A PAIR OF FIXED CONTACTS, SUPPORT MEANS FOR SAID VANE AND FIXED CONTACTS, A CONTACT CARRIED BY SAID VANE AND POSITIONED FOR ENGAGEMENT WITH ONE OF SAID FIXED CONTACTS WHEN THE VANE IS ONE STABLE POSITION, A SECOND CONTACT CARRIED BY SAID VANE AND POSITIONED FOR ENGAGEMENT WITH THE OTHER OF SAID FIXED CONTACTS WHEN 